How to attach tall cupboards onto 40mm thick plaster

[Doran]

I will be placing some tall cupboards (2m30ish in total) against a wall. (library image below)
They need to have attachment points at the top, into our plasterboard to stop them toppling. They are 'not' weight bearing.

Did a quick test drill; the wall is 40mm plaster (I presume acoustic plaster as it's a new(ish) build), with only 5mm cavity before the brick.
Whats your best way for attaching to the plaster?

Thanks

 

[opps]

If you were hanging shelve/etc., I would use Corefix

https://www.sccrewfix.com/p/corefix-metal-plastic-100-heavy-duty-dot-dab-wall-fixing-10-x-95mm-24-pack/344hg

Technically they are designed for walls with plasterboard and a cavity not exceeding 45mm.

Given that you are only using the fittings as anti-tilt devices, I would just go with regular frame fixings.

Easyfix Frame Fixings 8 x 100mm 10 Pack

Order online at Screwfix.com. Nylon fixings for fixing timber to masonry. Heavy ribbing ensures a tight hold in aerated blocks. FREE next day delivery available, free collection in 5 minutes.

www.screwfix.com

BTW, if you drill downward at a slight angle, you will increase the shear loading.

 

[Dereekoo]

BTW, if you drill downward at a slight angle, you will increase the shear loading.

But since the cupboards aren't imposing shear loads on the fixing it doesn't matter

 

[foxhole]

90mm screws, nothing special required unless it’s into thermalite blocks.

 

[opps]

But since the cupboards aren't imposing shear loads on the fixing it doesn't matter

True but if a small child decided to use the units as a climbing frame there would be a shear load.

 

[Deleted member 174758]

True but if a small child decided to use the units as a climbing frame there would be a shear load.

5 x 90 or 100mm into a brown plug (7mm) into the underlying masonry will be a stronger fix than any fixing which depends on the strength of the dry lining materials (plasterboard) and is a lot cheaper than Corefix, etc. Angle the drill downwards by 10 to 15 degrees to give increased pull-out resistance

 

[opps]

5 x 90 or 100mm into a brown plug (7mm) into the underlying masonry will be a stronger fix than any fixing which depends on the strength of the dry lining materials (plasterboard) and is a lot cheaper than Corefix, etc. Angle the drill downwards by 10 to 15 degrees to give increased pull-out resistance

I agree about drilling downwards but if the masonry is 45mm from the surface, surely the plug risks being pulled towards the surface as you tighten the screw?

Wow, I think this is the first time that I have ever disagreed with you.

I need to sit down....

 

[Dereekoo]

I agree about drilling downwards but if the masonry is 45mm from the surface, surely the plug risks being pulled towards the surface as you tighten the screw?

Wow, I think this is the first time that I have ever disagreed with you.

I need to sit down....

Agree that pull out resistance will be increase but as long as drilled hole is the right diameter as soon as you start screwing into it the plug will expand and bite into wall. I usually lightly hammer the screw in before screwing so the plug expands and grips straight away even if hole is slightly oversized. Back to any shear force, since the cupboards are supported off the floor no loads, climbing kids or sacks of potatos etc etc, will create a shear force.

 

[Deleted member 174758]

@opps, your Easyfix or Corefix screws won't go any further into the masonry than a 5 x 100mm wood screw, and you cannot really guarantee that the PB will give you any extra support (especially if the PB were old/soft/ had been allowed to absorb moisture in the past, etc), so you are really depending on 35mm or so of plug (assuming a "standard" brown plug) with the screw going another 5 to 10mm beyond that in the hole. So how much difference (other than a massive difference in price) is there between the performance of a long 5mm screw in a plug and, say, a Corefix?

If a screw is properly tighten it into a plug it will wedge itself in the hole; if the hole is angled downwards slightly should the furniture be pulled away from the wall being slightly tilted should further wedge the screw into the hole. That's certainly why sign fitters use long screws and angle them downwards a bit to secure fairly shallow light boxes.

As an aside I did used to do a bit of fitting for a flat pack firm from time to time (weekends and evenings - a change from the day job!), including kids wardrobes and bunk beds. I always fixed the safety straps in the way I stated, and I used to try out the bunk beds for safety by standing on the lower frame and hanging outwards from the bed. I figured that if the screw wouldn't come out with my 85 to 90kg weight plus maybe 10kg of tool belt and boots hanging off it then a skinny 7 year old shouldn't be a problem for it

 

[Doran]

Thanks for the input everyone. But I gotta say, no potatoes will be hanging off these things, let alone kids. But some great advice nevertheless.
One thing to note, the attachment is inside of the bookcase, in the corners, so no real option there for an angled drill hole. But I will see if there's some other option, just in case

 

[Deleted member 174758]

Just make sure that your plugs are snug in the holes and that your screws aren't too small and are in tight as well

 

[opps]

Just make sure that your plugs are snug in the holes and that your screws aren't too small and are in tight as well

Sorry I am confused. The OP has 40mm of insulated plasterboard, with a 5mm cavity behind it.

If he dills a 7mm hole and pushes a brown plug in, then surely he is relying on the plug expanding in polystyrene or celotex (or similar)?

Do you mean that he should punch the plug through the plasterboard and cavity, in to the block work?

I have done that in the past and found that as I tightened the screw, it just pulled the plug forward.

 

[foxhole]

Sorry I am confused. The OP has 40mm of insulated plasterboard, with a 5mm cavity behind it.

If he dills a 7mm hole and pushes a brown plug in, then surely he is relying on the plug expanding in polystyrene or celotex (or similar)?

Do you mean that he should punch the plug through the plasterboard and cavity, in to the block work?

I have done that in the past and found that as I tightened the screw, it just pulled the plug forward.

No insulation mentioned, just plasterboard which you always ignore when fixing, plug goes into block or brick and there is zero pull force when you screw into a plug unless you drilled too shallow and screw hits brickwork it which case it will remove plug.

 

[opps]

No insulation mentioned, just plasterboard which you always ignore when fixing, plug goes into block or brick and there is zero pull force when you screw into a plug unless you drilled too shallow and screw hits brickwork it which case it will remove plug.

The OP says that the plaster is 40mm thick with a 5mm cavity behind it. The OP seems to think that it is acoustic plasterboard, I suspect that it may be insulted plasterboard.

In my experience, when driving a screw in to a nylon plug, as the screw thread cuts in to the nylon, it pulls the plug up the thread. If drilling directly in to a brick, using a screw and plug (and no other fittings), it is not an issue In the case of fitting a timber baton (etc) to a wall, because the baton is against the wall the plug is prevented from pulling out of the wall because it butts up to the baton. The principle of expansion then secures the fitting and baton.

In order to bury a plug, it needs to be collarless, unless you are planning to drill a wider hole in the plasterboard and a small diameter hole in the blockwork. If the expansion effect has not kicked in before you finish tightening the screw, it will definitely pull the plug out, particularly if the bricks are fairly soft.

That said, in this case, if the OP's fittings are the type where you drive the screw most of the way home, then drop the rectangular plate with the keyhole cut in it over the top of the screw and then finish tightening the screw it may be OK provided that a sufficient amount of the screw had passed through the plug to ensure expansion.

IMO, using frame fixings is more reliable. Additionally, they will not pull the plasterboard in towards the cavity

 

[foxhole]

The OP says that the plaster is 40mm thick with a 5mm cavity behind it. The OP seems to think that it is acoustic plasterboard, I suspect that it may be insulted plasterboard.
Plug collarless or not are easily buried in hole .
In my experience, when driving a screw in to a nylon plug, as the screw thread cuts in to the nylon, it pulls the plug up the thread. If drilling directly in to a brick, using a screw and plug (and no other fittings), it is not an issue In the case of fitting a timber baton (etc) to a wall, because the baton is against the wall the plug is prevented from pulling out of the wall because it butts up to the baton. The principle of expansion then secures the fitting and baton.

In order to bury a plug, it needs to be collarless, unless you are planning to drill a wider hole in the plasterboard and a small diameter hole in the blockwork. If the expansion effect has not kicked in before you finish tightening the screw, it will definitely pull the plug out, particularly if the bricks are fairly soft.

That said, in this case, if the OP's fittings are the type where you drive the screw most of the way home, then drop the rectangular plate with the keyhole cut in it over the top of the screw and then finish tightening the screw it may be OK provided that a sufficient amount of the screw had passed through the plug to ensure expansion.

IMO, using frame fixings is more reliable. Additionally, they will not pull the plasterboard in towards the cavity

No pull force exists when drive a screw into plug , all the force is towards the wall, frame fixings are very poor at resisting pull force and can easily be pulled out, they are intended to resist lateral force .Plugs regardless of collar can be buried in the hole.